CN1945757B - MgB2 composite superconductive wire (band) material and its preparing method - Google Patents

Abstract

This invention relates to a MgB2 compound super-conducting wire and its preparation method characterizing that a Fe2O3 blocking layer is set between the MgB2 core of the MgB2 super-conduction wire and the iron base, before preparation, the internal part of an iron tube is cleaned and heated in boiling distilled water for 10-30 minutes, the iron tube is taken out and put in a dried close containerand the FeO film on the surface of the iron tube is removed after the moisture is evaporated, then commercial Mg powder is mixed with B powder to be put in the tube to be sealed, then multiple iron tubes are put in a large aperture tube to constitute a compound tube, which is swaged and the powder in it is tamped, then the tube is cold-drawn to a long wire by a drawing machine or cold-rolled to aflat strip with a rolling machine then to be winded on a ceramic framework and put in a reaction oven with 900-1000deg.C Ar gas protection to be heat-processed for 0.5-1 h to resume the temperature naturally.

Description

A kind of MgB 2Composite superconducting wire (band) material and preparation method thereof

Technical field

The present invention relates to MgB ₂Superconducting line (band) material and preparation method thereof.

Background technology

In January calendar year 2001, the critical transition temperature that people such as Japanese scientist Akimitsu find is the MgB of 39K ₂Superconductor has caused global extensive concern.MgB ₂Created the new record of intermetallic compound superconductor critical temperature,, made one of its principal focal point that becomes current superconduction research because it combines the simplicity of high-critical temperature and compound.Though MgB ₂The critical temperature of superconductor only is 39K, but different with oxide high temperature superconductor, MgB ₂Have foolproof chemical composition and crystal structure, the cost of material is very low, become a useful person easily, and the electric current that the crystal boundary energy carrying is very high, its intrinsic Jc is very high (to surpass 10 ⁷A/cm ²While MgB ₂Coherence length bigger than the oxide coherence length of perovskite structure, this just means MgB ₂In be easier to introduce useful flux pinning center, improve superconductivity.MgB ₂Can just realize using at liquid hydrogen warm area (20K-30K), and cryogenic superconductor can't be worked at this warm area, the liquid hydrogen warm area just can obtain need not complicated and expensive liquid helium easily by refrigeration machine.Comprehensive refrigeration cost and material cost, MgB ₂Superconductor is at 20-30K, and low field condition is used the price advantage that has clearly down, especially in MRI magnet (work magnetic field 1-2T) field.This also is MgB in the world ₂One of key reason that superconductor applications research is persistently overheating.In addition, also be with a wide range of applications at aspects such as superconducting power (hyperconductive cable, superconducting transformer, superconductive current limiter etc.), electronic device and national defence.

In recent years, people had ined all sorts of ways and had prepared various MgB ₂Wire strip.Because MgB ₂Material is hard and very crisp, can not process by standard machinery and make wire rod, up to the present, mainly contains three kinds and prepares MgB ₂The method of band: (1) powder-in-tube technique (PIT), 2) two-step method: be equipped with the B/Ta base band with the electrophoresis legal system, under the vapour pressure condition of Mg, anneal then.(3) diffusion method: B is diffused in the Mg band or Mg is diffused in the B band.Present wire/belt material research all concentrates on powder tubulature (PIT) technology, and this is because powder swabber artistic skill is easy to be generalized in the large-scale industrial production.Preparation MgB ₂The typical process flow of wire rod is as follows: the MgB of forerunner's powder → be encapsulated into iron jacket → composition multiple tube → swage → drawing → rolling → annealing → moulding ₂Wire rod, as shown in Figure 1.In the selection of sheath material, mainly be the reaction of considering core and sheath material.Studies show that the selection of best sheath material should be the Fe pipe, secondly is stainless steel tube.Adopt the PIT technology can produce multicore MgB ₂Composite wire improves critical current, has improved the mechanical strength of wire rod simultaneously.

Superconductor resistance under the DC operation condition is zero, does not have joule loss.But by alternating current or when being in the alternating magnetic field, magnetic flux constantly penetrates into and withdraws from superconductor; The turnover of this magnetic flux, magnetic flux must overcome flux pinning force and magnetic flux flow resistance, thereby consumed energy, and this loss is referred to as magnetic hysteresis loss.Magnetic hysteresis loss can reduce by the silk footpath that reduces superconducting core.In order to improve the stability of composite superconducting wire, the zone of superconducting core is by the material encirclement-base material of high thermal conductance and conductivity, is decomposed into the compound MgB of bandlet cross section and circular cross-section as Fig. 2 and Fig. 3 ₂Schematic cross-section.In superconducting line, when making local running current surpass critical current for a certain reason,, increase the overcurrent of superconductor and the stability of heat by the base material bypass.Simultaneously, adopt composite conductor, can also increase the mechanical strength of superconducting wire.

Under the alternating magnetic field environment, coupling produces couple current between superconduction multicore composite strip generation core; And be the normal metal material between core, the couple current cross-current is through metallic substrates, thus generation coupling loss.The coupling A.C.power loss is the significant obstacle of restriction composite superconductor AC applications.Along with MgB ₂How the continuous maturation of compound long line production technology reduces the A.C.power loss that is coupled, and is the technology of being badly in need of solution at present.

Present MgB ₂The method of superconduction multicore composite strip preparation still adopts traditional Nb ₃Sn, preparation (PIT) technology of Bi system high-temperature superconducting multicore band-powder tube dress law technology.This technology comparative maturity in the pipe, carries out drawing, heat treatment but it is directly packed superconductive powder such as Bi2223 or MgB2 powder into.Superconducting core directly contacts with metal base material, makes the composite superconductor transverse resistivity very low, and under the AC applications situation, the induction couple current is serious, has increased coupling loss.

Summary of the invention

The objective of the invention is to overcome the higher shortcoming of prior art superconduction multicore composite strip coupling A.C.power loss, a kind of MgB2 composite superconducting wire (band) material and preparation method thereof is provided.

MgB of the present invention ₂Composite superconducting wire (band) material is between superconducting core and normal metal base material, forms one deck iron oxide high resistivity barrier layer.This barrier layer parcel superconducting core, thickness is 0.1 μ m-1 μ m.The resistivity on barrier layer is than the big 2-3 of an iron order of magnitude, and fusing point reaches 1600 ℃.

MgB of the present invention ₂Composite superconducting wire (band) material is not change the long line MgB of original powder tube dress method (PIT) production ₂Be prepared under the prerequisite of technology.The preparation raw material are that purity is, granularity is 1 μ m--50 μ m Mg powder and purity are, granularity is the B powder of 0.1-5 μ m more than 99% more than 95%.Before the iron pipe of packing into, the aquae destillata of iron pipe with boiling heated iron pipe, take out after 10-30 minute, place dry container to dry, so that form the oxide of iron at the iron pipe surfaces externally and internally.Typical process flow is as follows: the MgB of iron jacket → composition multiple tube that forerunner's powder → be encapsulated into boiling water heated → swage → drawing → rolling → annealing → moulding ₂Wire rod.

Concrete grammar is: forerunner Mg and B powder are put into mixed reaction vessel, and full and uniform mixed compacting was inserted in 650-900 ℃ the reacting furnace of argon atmosphere protection reaction 0.5-3 hour, formed stable MgB ₂Material; With MgB ₂The material taking-up is put into ball mill and is ground, and is prepared into the MgB that granularity is 0.1-50 μ m ₂Powder is so-called ripe powder, then ripe powder is packed in the iron pipe of crossing with above PROCESS FOR TREATMENT, and compacting is carried out cold drawing (circular section wire forming) with drawbench, then carries out cold bundle (shaping of flat cross section band) with the bundle machine.Put into the heating furnace of temperature 900-1000 ℃ argon atmosphere at last and heat-treat, the time is 0.5-1 hour; Then rise again naturally, promptly prepare low AC loss MgB with barrier layer ₂Iron-based superconduction wire/belt material.

In a word, the invention provides a kind of preparation MgB ₂The method of composite superconducting wire or band, with commercially available purity be more than 99%, granularity is the Mg powder of 1 μ m-50 μ m, the B powder that with purity be more than 95%, granularity is 0.1 μ m-5 μ m is evenly mixed, pack in the iron pipe, sealing iron pipe, the iron pipe of many sealings is packed in the heavy caliber iron pipe, form multiple tube; Multiple tube is swaged, powder in the compacting pipe, again with the round line of drawbench cold drawn growth, or with the cold rolling bandlet of making of roll mill; The wire-wound of rolling band or cold drawn one-tenth on ceramic skeleton, is put into the reacting furnace of 900-1000 ℃ argon atmospher protection and was heat-treated 0.5-1 hour, stop heating after, it is risen again naturally, it is characterized in that preparing MgB ₂Before wire rod or the band, earlier iron pipe inside is cleaned up, the distilled water of putting into boiling heated 10-30 minute, take out iron pipe, place dry closed container, treat the iron pipe water evaporates after, form the sull of high resistivity on the surface of first iron pipe and second iron pipe.

The present invention also provides a kind of MgB that makes according to above-mentioned method ₂Composite superconducting wire or band comprise at the bottom of MgB2 core and the iron-based, it is characterized in that at MgB ₂The iron oxide barrier layer that high resistivity is arranged between at the bottom of core and the iron-based.

Preferably composite superconducting wire or band are circular section wire rod, square-section band or oval cross section wire rod.

Preparation method's of the present invention principle is:

Though adopt the multiple-core technology, can reduce magnetic hysteresis loss, improve dynamic stability.But exchange or in the alternating magnetic field environment being connected with, can in the substrate material of composite superconductor, induce eddy current field, it forms the loop by the base material that superconducting core is horizontally through normal metal, and the eddy current field that induces produces the couple current of closed-loop path between superconducting core and normal metal base material.Under horizontal alternating magnetic field situation, being distributed in of couple current do not have resistance in the superconducting core, but because base material is the normal metal material, has resistance, thereby produces coupling loss.Coupling loss under the alternating magnetic field in the composite superconductor is (1)

$P_c=\frac{2\mathrm{\τ}}{{\mathrm{\μ}}_0}{\left(\frac{d{B}_e}{\mathrm{dt}}\right)}^2---\left(1\right)$

τ is coupling time Changshu in the formula, B _eIt is external magnetic field.

$\mathrm{\τ}=\frac{{\mathrm{\μ}}_0{L}_p^2}{16{\mathrm{\ρ}}_{\mathrm{eff}}}\frac{d_c^2}{w_c^2}---\left(2\right)$

w _cAnd d _cBe respectively the width and the thickness (w in band superconducting core zone _c＞＞d _c), L _pIt is the moment of torsion of superconducting core.ρ _EffIt is the horizontal effective resistivity of complex superconducting strip substrate sheath material.

Directly being embedded in the substrate sheath material for superconducting core in the composite strip is that superconducting core and substrate sheath material have good electrical contact, complex effective resistivity ρ _EffFor

${\mathrm{\ρ}}_{\mathrm{eff}}={\mathrm{\ρ}}_m\frac{1-{\mathrm{\η}}_{\mathrm{eff}}}{1+{\mathrm{\η}}_{\mathrm{eff}}}---\left(3\right)$

If have insulation barrier between superconducting core and the substrate sheath material in the composite strip, complex effective resistivity ρ _EffFor

${\mathrm{\ρ}}_{\mathrm{eff}}={\mathrm{\ρ}}_m\frac{1+{\mathrm{\η}}_{\mathrm{eff}}}{1-{\mathrm{\η}}_{\mathrm{eff}}}---\left(4\right)$

Here ρ _mBe the resistivity of substrate sheath material, η _EffIt is the volume ratio that the superconducting core zone accounts for whole composite conductor.

By equation (1) and (2) as can be seen, coupling loss and frequency square is directly proportional.Therefore, frequency is high more, and coupling loss is big more; Be inversely proportional to the effective resistivity of composite material.By (3) and (4) as can be known, it is more much bigger than the effective resistivity that has insulation barrier between superconducting core and the base material that superconducting core directly is embedded in the interior effective resistivity of metal base.Therefore between superconducting core and base material, increase high resistivity material, can greatly reduce the coupling loss under the interchange situation.

The present invention is based between superconducting core and metal base and produces high resistance barrier, thereby the technology of increase composite superconductor transverse resistivity reduces the purpose of coupling loss.

Description of drawings

Fig. 1 is MgB ₂The technological process of production schematic diagram of long line powder tube dress method PIT;

Fig. 2 is MgB ₂The flat schematic cross-section of long line;

Fig. 3 is MgB ₂Long line circular section schematic diagram;

Fig. 4 adorns MgB ₂Iron pipe treatment process schematic diagram before the powder;

Fig. 5 a is existing iron jacket list core MgB ₂Compound wire/belt material schematic cross-section;

Fig. 5 b is iron jacket list core MgB of the present invention ₂Compound wire/belt material schematic cross-section;

The multicore MgB that the existing powder tube dress method of Fig. 6 a is produced ₂The circular cross-section schematic diagram of composite superconducting wire;

The multicore MgB that Fig. 6 b the inventive method is produced ₂The circular cross-section schematic diagram of composite superconducting wire;

The multicore MgB that the existing powder tube dress method of Fig. 6 c is produced ₂The bandlet schematic cross-section of composite superconducting wire;

The multicore MgB that Fig. 6 d the inventive method is produced ₂The bandlet schematic cross-section of composite superconducting wire.

Embodiment

At preparation MgB of the present invention ₂Before line (band) material, earlier the iron pipe inside and outside is cleaned impurity such as oil stain, dust inside and outside the iron pipe with organic solvent such as ether, make the iron pipe integral surface clean and tidy, totally get final product.After treating that the organic solvent volatilization finishes, the distilled water of putting into boiling heated 10-30 minute, as shown in Figure 4.Take out iron pipe then, be placed in the dry closed container, wait the iron pipe water evaporates after, form sull at the surfaces externally and internally of iron pipe, shown in Fig. 5 b.

According to following technological process: forerunner's powder → be encapsulated into is in the iron pipe of crossing through boiling water treating → form the MgB of multiple tube → swage → drawing → rolling → annealing → formation moulding ₂The preparation technology of wire/belt material.Concrete processing step is as follows:

With commercially available purity be more than 99%, granularity is the Mg powder of 1-50 μ m; the B powder that with purity be more than 95%, granularity is 0.1-5 μ m is put into mixed reaction vessel; full and uniform mixed compacting; insert in 650-900 ℃ the reacting furnace of argon atmosphere protection reaction 0.5-3 hour, and formed stable MgB ₂Material; With MgB ₂The material taking-up is put into ball mill and is ground, and being prepared into granularity is the ripe powder of MgB2 of 0.1-50 μ m, ripe powder is packed in the iron pipe that the distilled water of boiling was handled sealing iron pipe.Then many sealing iron pipes are packed in the heavy caliber iron pipe, form multiple tube.Multiple tube is swaged powder in the compacting pipe.Again with the round line of drawbench cold drawn growth, or with the cold rolling bandlet of making of roll mill.Rolling band or wire-wound on ceramic skeleton, are put into the reacting furnace of 900-1000 ℃ argon atmospher protection and heat-treated 0.5-1 hour.Concrete temperature and time is chosen does not have strict restriction.Heat treatment temperature is high more, and the used time is short more.As heat treatment temperature is 750 ℃, and then heat treatment time was 0.5-0.8 hour scope; As heat treatment temperature is 950 ℃, and then heat treatment time is 1000 ℃ 0.3-0.5 hour scope as heat treatment temperature; Then heat treatment time is 0.3-0.4 hour scope.After stopping heating, it is risen again naturally, so far just finish compound iron jacket multicore MgB ₂The preparation of line (band) material.

Embodiment 1: with commercially available purity be more than 99%, granularity is the Mg powder of 50 μ m; the B powder that with purity be more than 95%, granularity is 2.5 μ m is put into mixed reaction vessel; full and uniform mixed compacting was inserted in 650 ℃ the reacting furnace of argon atmosphere protection reaction 3 hours, formed stable MgB ₂Material; With MgB ₂The material taking-up is put into ball mill and is ground, and being prepared into granularity is the ripe powder of MgB2 of 50 μ m, ripe powder is packed in the iron pipe that the distilled water of boiling was handled sealing iron pipe.Then many sealing iron pipes are packed in the heavy caliber iron pipe, form multiple tube.Multiple tube is swaged powder in the compacting pipe.Again with the round line of drawbench cold drawn growth, or with the cold rolling bandlet of making of roll mill.Rolling band or wire-wound on ceramic skeleton, are put into the reacting furnace of 950 ℃ argon atmospher protection and heat-treated 0.6 hour.After stopping heating, it is risen again naturally, so far just finish compound iron jacket multicore MgB ₂The preparation of line (band) material.

Embodiment 2: with commercially available purity be more than 99%, granularity is the Mg powder of 5 μ m; the B powder that with purity be more than 95%, granularity is 5 μ m is put into mixed reaction vessel; full and uniform mixed compacting was inserted in 900 ℃ the reacting furnace of argon atmosphere protection reaction 0.5 hour, formed stable MgB ₂Material; With MgB ₂The material taking-up is put into ball mill and is ground, and being prepared into granularity is the ripe powder of MgB2 of 5 μ m, ripe powder is packed in the iron pipe that the distilled water of boiling was handled sealing iron pipe.Then many sealing iron pipes are packed in the heavy caliber iron pipe, form multiple tube.Multiple tube is swaged powder in the compacting pipe.Again with the round line of drawbench cold drawn growth, or with the cold rolling bandlet of making of roll mill.Rolling band or wire-wound on ceramic skeleton, are put into the reacting furnace of 750 ℃ argon atmospher protection and heat-treated 0.8 hour.After stopping heating, it is risen again naturally, so far just finish the preparation of compound iron jacket multicore MgB2 line (band) material.

Embodiment 3: with commercially available purity be more than 99%, granularity is the Mg powder of 1.5 μ m; the B powder that with purity be more than 95%, granularity is 1.5 μ m is put into mixed reaction vessel; full and uniform mixed compacting was inserted in 750 ℃ the reacting furnace of argon atmosphere protection reaction 1 hour, formed stable MgB ₂Material; With MgB ₂The material taking-up is put into ball mill and is ground, and being prepared into granularity is the ripe powder of MgB2 of 1.5 μ m, ripe powder is packed in the iron pipe that the distilled water of boiling was handled sealing iron pipe.Then many sealing iron pipes are packed in the heavy caliber iron pipe, form multiple tube.Multiple tube is swaged powder in the compacting pipe.Again with the round line of drawbench cold drawn growth, or with the cold rolling bandlet of making of roll mill.Rolling band or wire-wound on ceramic skeleton, are put into the reacting furnace of 1000 ℃ argon atmospher protection and heat-treated 0.4 hour.After stopping heating, it is risen again naturally, so far just finish compound iron jacket multicore MgB ₂The preparation of line (band) material.

MgB according to the inventive method preparation ₂Composite superconducting wire (band) material is naturally at MgB ₂Between at the bottom of core and the iron-based, produce the iron oxide high resistance barrier, shown in Fig. 5 b.The iron jacket list core MgB of existing prepared shown in Fig. 5 a ₂Compound wire/belt material, the circle of the existing prepared shown in Fig. 6 a and Fig. 6 c and the compound MgB of bandlet tee section ₂Split conductor/carrying material, the MgB of above art methods preparation ₂Line (band) material does not all have the iron oxide high resistance barrier.Fig. 6 b and Fig. 6 d are the circle and the compound MgB of bandlet tee section of the inventive method preparation ₂Split conductor/carrying material is at MgB ₂Form the iron oxide high resistance barrier between at the bottom of core and the iron-based.The barrier layer of this high resistivity has greatly increased the transverse resistivity of compound wire, and coupling loss is reduced greatly.MgB of the present invention ₂The resistivity on iron oxide barrier layer is at room temperature than the high 2-3 of the resistivity order of magnitude of iron in composite superconducting wire (band) material: the resistivity of iron is 9.8 μ Ω cm, and iron oxide resistivity at room temperature is 10 ^-1-10 ^-3Ω cm.This barrier resistance rate is more than 100 times of iron.Therefore the thickness on barrier layer is about μ m magnitude, and the high resistivity barrier layer that forms between at the bottom of superconducting core and the iron-based can greatly increase the horizontal composite resistivity of superconducting tape, and then has reduced eddy current loss and coupling loss under the ac operation situation.

Simultaneously, because the fusing point height of iron oxide, decomposition temperature is about 1600 ℃, and the reaction temperature of Mg and B is about 900 ℃, in the heat treatment process after the powder tube dress is finished, iron oxide not can with Mg, B or MgB ₂Reaction, ferriferous oxide can not pollute MgB yet ₂, can not produce any influence to its superconductivity.

MgB of the present invention ₂Composite superconducting wire (band) material can be the circular section line, also can be square-section band or flat section line.

Claims (3)

1. prepare MgB ₂The method of composite superconducting wire or band, with commercially available purity be more than 99%, granularity is the Mg powder of 1 μ m-50 μ m, the B powder that with purity be more than 95%, granularity is 0.1 μ m-5 μ m is evenly mixed, pack in the iron pipe, sealing iron pipe, many sealing iron pipes are packed in the heavy caliber iron pipe, form multiple tube; Multiple tube is swaged, powder in the compacting pipe, again with the round line of drawbench cold drawn growth, or with the cold rolling bandlet of making of roll mill; The wire-wound of rolling band or cold drawn one-tenth on ceramic skeleton, is put into the reacting furnace of 900-1000 ℃ argon atmospher protection and was heat-treated 0.5-1 hour, stop heating after, it is risen again naturally, it is characterized in that preparing MgB ₂Before wire rod or the band, earlier iron pipe inside is cleaned up, puts into distilled water heating 10-30 minute of boiling, take out iron pipe, place dry closed container, treat the iron pipe water evaporates after, form the sull of high resistivity on the surface of iron pipe.

2. MgB who makes according to the method for claim 1 ₂Composite superconducting wire or band comprise MgB ₂At the bottom of core and the iron-based, it is characterized in that at MgB ₂The iron oxide barrier layer that high resistivity is arranged between at the bottom of core and the iron-based.

3. MgB according to claim 2 ₂Composite superconducting wire or band is characterized in that composite superconducting wire or band are circular section line or square-section band or flat section line.

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